In the field of flow control systems, one technique for providing chilled process water to a plurality of remote sites is to use a primary flow loop from chillers to the sites where the water is to be utilized, as for air cooling, and then back to the chillers for recycling in a continuous cycle of operation. At the remote sites where the process water is to be used, secondary flow loops tap from, and return to, the primary loop, the chilled water for use in air cooling at each of the various sites. As a result, there is one primary loop in a continuous flow and a plurality of secondary loops for utilizing the water from the primary loop as needed.
In considering any one secondary loop, there will be a section of crossover line which is common with both the primary loop and the secondary loop. The apparatus coupling the primary loop with a secondary loop is a water bridge. A primary pump is used to continuously feed the water through the primary loop. A secondary loop is used to feed the water through each secondary loop but only at a given rate and only when required. Without appropriate controls, however, the system would be very inefficient, chilling and/or feeding more or less water than is needed for the intended air cooling.
In U.S. Pat. No. 3,729,051, the problem of controlling the quantity of flowing water was addressed and solved. According to that patent, a small supplemental water line is placed across the common extent of the primary and each secondary loop. The supplemental line at each secondary loop was of a significantly smaller diameter for a limited flow, merely sufficient to sense a primary flow balance between the primary loop and the flow of the secondary loop.
For optimum efficiency the flow through the primary loop should equal the flow through the total of secondary loops. If insufficient water is pumped in either loop, the intended cooling will not be effected. If excess water is pumped, unnecessary energy will be expended in moving the water. By sensing the flow along the supplemental line, verification may be made that water is flowing and that pressure exists in the supplemental line. So long as the sensed water in the supplemental line remains at the optimum predetermined flow, no change is made to the fluid flow. If, however, the sensed water varies from the predetermined flow, a signal is sent back to a first control valve in the primary loop to restrict the flow and thereby minimize the work done by the pump of the primary loop. This effects a greater efficiency.
In a subsequent improvement, as described in the U.S. Pat. No. 3,875,995, temperature is also taken into account for controlling water flow. In the event that the water in the secondary loop varies from its intended, predetermined temperature, inefficiency results. If the temperature of the water in the secondary loop is not cool enough, the intended air cooling will not be effected. If the temperature of the water in the secondary loop is too cool, excess chilling is being done at an unnecessary cost to the system and its user. As a result, a temperature control sensor is provided. So long as the sensed temperature is at a predetermined value, the chilling simply continues. If, however, the temperature deviates from the predetermined value, the difference is sensed and a signal is sent to a second control valve located in the crossover line of the water bridge to vary the quantity of chilled water provided to the secondary loop. This feature further increases the efficiency of the system.
In a third improvement to fluid control systems, as described in the copyrighted BRDG-TNDR Corporation brochure of 1988, the signals generated for temperature and pressure control are fed back from the water bridges of the air cooling subassemblies to the water chiller subassembly to vary the amount of recirculating water being fed through the chiller to thereby modify the temperature and pressure of the water in the primary loop. By keeping the water in the primary loop at a preselected temperature and pressure for a particular application further efficiencies are effected in the system.
The present invention, in its simplest terms, is on improvement over known flow control systems in that the temperature and pressure sensors are replaced with electronic sensors of a size and capability more efficient than those previously known and utilized. Their use in the lines of fluid flow, as described above, not only generate more accurate readings but have less effect on the flow. This further increases the accuracy of readings and provides greater control and efficiency in the system. In addition, each temperature sensor is removed from the site of sensing and repositioned with its controller adjacent to its controlled valve. As such, all electronic controls for each secondary loop are integrated into a common controller for greater overall efficiency. This more readily allows all the controllers for all the secondary loops to be in two-way communication with a common host computer for integration of the system generally. As such, the efficiencies effected to the system are greater than the sum of the efficiencies of the individual water bridges.
As referred to above, the prior art discloses systems for controlling the flow of process fluids. Nothing in the prior art, however, controls the flow with the accuracy and efficiency afforded by the present invention.
Therefore, it is an object of this invention to provide a method and apparatus which overcomes the aforementioned shortcomings and which is a significant contribution to the advancement of the arts.
It is a further object of this invention to integrate the flow controller and sensor of a water bridge into a single component.
It is yet a further object of this invention to allow the flow controller of a water bridge to use one of several means as its driver to allow for applications with various fluids under various operating conditions, i.e. high and low temperatures, high and low pressures, viscous and nonviscous, clean and dirty, etc.
Another object of the invention is to provide controllers/sensors with two-way communications for the purpose of talking with a host computer and data acquisition equipment to thereby allow for control reset, control limits, systems management, trending, historical data accumulation, etc.
A further object of the present invention is to poll the outputs of the water bridge controllers for the purpose of resetting the set points or control system pressures and temperatures.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.